Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first embodiment of a display screen or portion thereof with graphical user interface, showing the new design;

FIG. 2 is a second embodiment thereof; and,

FIG. 3 is a third embodiment thereof.

The outermost broken line illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining broken lines represent elements of the display screen or portion thereof with a graphical user interface that form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 